The ID is just a system generated key to uniquely identify the lead in Marketo's database, it will keep incrementing as leads are added, but it shouldn't matter what the lead's ID is really. What are you trying to do?

Thanks for the reply!I just start using Marketo. Not sure what the first 11 leads are. Do you know where I can have a overview of all the leads in my Marketo database? Then I could manage the database?